Effect of processing conditions on wood and glass fiber length attrition during twin screw composite compounding

In this study, we compare the effect of twin-screw extrusion processing on the attrition of wood fibers (WFs) with glass fiber. The effects of process variables and screw design on fiber length were investigated by performing a range of dead-stop experiments where the extruder was stopped, opened-up, and compound removed from the screw elements. Fibers, chemically extracted from the polypropylene matrix, were analyzed for length and width using a commercial fiber analyzer. It was found that WF length attrition and composite properties were less affected by screw design and twin-screw processing conditions (feed rate and screw speed) than glass fiber. Length weighted fiber length and X50 length (a measure used in particle size analysis) were equally correlated with process conditions and composite performance for both fiber types. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48551.     

纤维素直接转化为乙酰丙酸的反应过程研究进展

综述了近年来纤维素在不同催化体系中制备乙酰丙酸的国内外研究进展,重点阐述了离子液体体系催化纤维素制备乙酰丙酸。分析指出了目前催化体系下生物质资源直接制备乙酰丙酸很难实现大规模工业化的原因,并对未来纤维素制备乙酰丙酸的研究重点进行了探讨和展望。     

纳米微晶纤维素的表面基团及其改性

纳米微晶纤维素(Nanocrystalline Cellulose,NCC)是一种纤维素经酸水解后获得的棒状晶体,由于其原料丰富、可再生、生物兼容性好以及机械性能优良等特点,已成为纳米材料研究领域的热点。本文为探索其进一步改性应用,重点分析了NCC表面存在的基团种类,对其化学改性方法进行了概括,并对其进一步发展应用进行了展望。     

纳米无机氧化物催化合成乙酸正丁酯

以冰乙酸和正丁醇为原料,纳米ZnO为催化剂催化合成乙酸正丁酯,探讨催化剂用量、酸醇物质的量比、反应时间等对反应结果的影响,对合成的产物进行红外光谱分析。结果表明,当酸醇物质的量比为1∶2.0,催化剂用量为0.8g(冰乙酸用量为0.1mol),反应温度为91～116℃,反应回流时间为3.0h,其酯化率可达86.72%。     

一株纤维素酶酶学特性的研究

通过对纤维素酶在两种不同底物中的酶解和糖化情况分别进行研究，确定该酶酶活力最高时的温度和pH（最适温度和最适pH），同时对酒精在纤维素降解过程中所产生的阻遏作用进行了初步的探讨。     

Microorganisms and Cellulose Digestion in the Gut of the Woodlouse Porcellio scaber

In the common woodlouse Porcellio scaber different parts of the gut were observed with respect to microbial counts, cellulose activity, and degradation of cellulose. Cellulose is mainly digested in the anterior part of the hindgut, as was indicated by the distribution of cellulolytic activity and the decrease of cellulose content inside the gut. The cellulases woodlice utilize for the degradation of litter are mainly produced by endosymbiotic bacteria in the hepatopancreas rather than by microorganisms ingested with the food. Microorganisms ingested with the litter are digested in the anterior part of the hindgut and may provide an important food source. In the posterior hindgut, bacterial proliferation ensures microbial colonization of feces.     

离子液体与树脂催化合成醋酸正丁酯的动力学比较

以阳离子交换树脂AMBERLYST15和各种离子液体为催化剂,研究了醋酸和正丁醇反应生成醋酸正丁酯的动力学。实验测定了催化剂种类、反应温度和催化剂量对反应速率的影响,并用拟均相模型对实验数据拟合。在实验条件下,发现AMBERLYST15和己内酰胺四氟硼酸盐催化效率很高,表观活化能分别为36.69,37.06kJ/g,指前因子分别为120.0,61.50m3/(g.h)。结果表明,树脂AMBERLYST15和己内酰胺四氟硼酸盐离子液体二类催化反应的活化能相近,指前因子却相差很大,2种催化剂在相同的催化机理下有不同的催化效率。     

P(AN-co-VAc)纤维的结构与性能研究

以醋酸乙烯酯(VAc)为第二单体,采用湿法纺丝制备了聚丙烯腈共聚物[P(AN-co-VAc)]纤维,并对其结构与性能进行了表征。结果表明:P(AN-co-VAc)纤维具有较好的热稳定性;随拉伸倍数增大,纤维结构变得致密,纤维的结晶、取向程度增大,玻璃化转变温度升高,纤维断裂强度增大,断裂伸长率降低。拉伸倍数为7时,P(AN-co-VAc)纤维的断裂强度达6.29cN/dtex,断裂伸长率为17%。     

聚乙二醇接枝聚醋酸乙烯酯的聚合动力学研究

以过氧-2-乙基己酸叔丁酯为引发剂,进行了聚乙二醇(PEG)存在下的醋酸乙烯酯(VAc)本体接枝聚合,考察了各VAc:PEG配比下聚合速率、PEG上PVAc的接枝率、PVAc的接枝效率、PEG的被接枝效率以及接枝共聚物的分子量随聚合时间的变化规律.结果发现,随配方中VAc配比的增加,聚合速率与极限转化率明显增加,聚合反应出现明显的自动加速现象;当VAc:PEG配比较大时,综合速率参数K随聚合时间不断上升,当VAc:PEG配比较低时,K随聚合时间呈下降趋势.各VAc:PEG配比下PVAc的接枝率几乎都随转化率的增大而线性地增加,接枝效率则几乎不随聚合时间而变;接枝率的大小正比于VAc:PEG配比,接枝效率则普遍较高,低VAc:PEG配比时,接枝效率可达95%以上;PEG的被接枝效率虽随转化率和VAc:PEG配比的增加而明显增加,但总体仍较低,表明聚合体系中有相当多一部分PEG未被接枝.高的VAc接枝效率和低的PEG被接枝效率表明,该Graft From接枝聚合体系中,可能存在着Graft Onto的接枝聚合机理.根据定义用来计算PEG-g-PVAc的数均分子量,发现随聚合转化率的增大而减小,并逐渐趋于常数,配方中VAc浓度越大越大;由GPC测试、PVAc普适校正计算发现,接枝聚合产物的分子量分布指数在1.5～2.5 之间,且随单体浓度和转化率的增加而增大.这些均与聚合体系的凝胶效应有关.